The present application is the U.S. national stage application of International Application PCT/GB99/02896, filed Sep. 2, 1999, which international application was published on Mar. 16, 2000 as International Publication WO 00/14554 A1 in the English language. The International Application claims the priority of British Patent Application 9818963.2, filed Sep. 2, 1998.
This invention relates to an arrangement for monitoring the operation of electrical circuits on a vehicle and, in particular, lamps or other electrical components on a vehicle trailer.
When a trailer (which may be for example a box trailer, a boat trailer or a caravan) is being towed by a vehicle, it is a legal requirement to equip the trailer with a set of rear warning lamps which duplicate the brake lamps, tail lamps and rear turn indicators of the towing vehicle. From time to time, a lamp on the trailer may fail, requiring, for example, the replacement of the lamp bulb. However, because trailer lamps are normally not visible to the driver, the driver may continue to drive unaware that a lamp has failed, which can be dangerous.
Although it is known to have lamp failure monitors for motor vehicle lamps, these are built into the circuitry of the motor vehicle, and therefore cannot be removed for use elsewhere.
According to the invention, there is provided apparatus for monitoring operation of electrical circuits on a vehicle trailer supplied with electrical power from a towing vehicle via a plug and socket wiring connector, the apparatus comprising a monitoring unit including means for outputting a signal in response to the failure of a component of a trailer electrical circuit; an indicator unit to be mounted in the towing vehicle in a position where it can give an indication to the vehicle driver, the indicator unit including means for indicating to the driver the failure of the component; and means for passing a component failure signal from the monitoring unit to the indicator unit, characterised in that the monitoring unit comprises a plug and socket adapted to be connected in series between the plug and socket otherwise used to connect the vehicle wiring to the trailer wiring, and the means for passing a component failure signal from the monitoring unit to the indicator unit is a radio transmitter and receiver.
The component may be a trailer or other trailer electrical component. The failure of a lamp or other component may be due, for example, to the failure of a bulb within a lamp, a fault with the connections to the socket holding the bulb the failure of a fuse, or any other discontinuity in the trailer circuitry associated with that component, and it will be understood that the term xe2x80x9ccomponent failurexe2x80x9d includes any such fault.
If one of the trailer components fails, the driver of the towing vehicle will be alerted and will be able to take the appropriate action to replace the component or otherwise correct the fault.
It may be convenient for the monitoring unit and indicator units to be separate units.
The transmitting means contained in the monitoring unit may have a range limited, depending on the system""s particular intended use, e.g. say to approximately five metres, sufficient to reach the indicator unit whilst avoiding undue interference with other equipment not on board the vehicle or trailer.
So that the monitoring unit can be easily connected into the electrical circuit powering the trailer electrical components, the monitoring unit may comprise a plug and socket adapted to be connected in series between the plug and socket otherwise used to connect the vehicle wiring to the trailer wiring. The plug and socket may be a standard 7-pin connection as is well known in respect of trailers being towed behind cars and vans. The invention can equally be applied to trailer systems which use different couplings; e.g. the coupling conventionally used on articulated lorries.
Such an arrangement allows the monitoring unit to be removed for use with different trailers or towing vehicles, since the plugs and sockets in existing use are normally standardised.
Means for releasably attaching the monitoring unit to either the towing vehicle or the trailer may be provided.
However, in a preferred embodiment, the monitoring unit comprises a clamp allowing it to be releasably attached to the tow arm of the trailer.
The plug of the monitoring unit connecting to the towing vehicle may be joined to the monitoring unit body via a short cable to allow the monitoring unit body to be positioned conveniently in or on the towing vehicle or trailer.
Since the monitoring unit can be exposed to rain and mechanical shock while the trailer is being towed, the electrical circuitry of the monitoring unit may be housed within a hard casing that is sealed. The casing may be fabricated from a suitable metal, with the inclusion of a non metallic window to allow for the transmission of radio signals from within the casing.
The indicator unit which alerts the driver to a component failure may have a front panel comprising a plurality of lights, each light being designated to turn on in response to a fault in a given trailer component or set of components, e.g., to allow the driver to identify the faulty component of components, the indicator panel may comprise markings or differently coloured lights such as light emitting diodes, for example. The indicator unit could alternatively or additionally emit a distinctive sound to warn of component failure, or provide some other indication to the driver.
The indicator unit may be placed in the driver""s compartment and may be powered from an on-board power socket, such as a cigarette lighter socket, for example. However, it is within the scope of the invention for the indicator unit to be powered by a battery housed within the unit.
The monitoring unit may comprise means for monitoring each of a number of trailer components continuously and, upon failure, passing a signal to a multichannel transmitter. However, if a multichannel transmitter is not available, the monitoring unit may comprises means for checking trailer components sequentially in a continuous cycle and, upon failure, passing a signal to a single channel transmitter.
Further examples of trailer electrical circuits that may require monitoring are the battery charging circuit on a caravan, which is powered from the electrical supply of the towing vehicle and refrigeration circuits on articulated lorries.